It would have made the def pbEndOfRoundPhase exit early, which means lines 3372 and later wouldn't ever run. This includes abilities that occur when a battler is switched in (e.g. weather), Truant's and Lock-On's counting down, and the cancelling of effects like flinching, Helping Hand, Charge, Magic Coat and Snatch (and a few others). This would result in some quirky behaviour, including a battler flinching from being attacked in the previous round, Pokémon always remaining Charged, and Regigigas never toggling between attacking and truanting.